Re: [RFC PATCH bpf-next 3/3] bpf, arm64: Optimize ADD,SUB,JMP BPF_K using arm64 add/sub immediates

[Daniel Borkmann]

On 5/7/20 3:05 AM, Luke Nelson wrote:
> The current code for BPF_{ADD,SUB} BPF_K loads the BPF immediate to a
> temporary register before performing the addition/subtraction. Similarly,
> BPF_JMP BPF_K cases load the immediate to a temporary register before
> comparison.
>
> This patch introduces optimizations that use arm64 immediate add, sub,
> cmn, or cmp instructions when the BPF immediate fits. If the immediate
> does not fit, it falls back to using a temporary register.
>
> Example of generated code for BPF_ALU64_IMM(BPF_ADD, R0, 2):
>
> without optimization:
>
>    24: mov x10, #0x2
>    28: add x7, x7, x10
>
> with optimization:
>
>    24: add x7, x7, #0x2
>
> The code could use A64_{ADD,SUB}_I directly and check if it returns
> AARCH64_BREAK_FAULT, similar to how logical immediates are handled.
> However, aarch64_insn_gen_add_sub_imm from insn.c prints error messages
> when the immediate does not fit, and it's simpler to check if the
> immediate fits ahead of time.
>
> Co-developed-by: Xi Wang <xi.wang@xxxxxxxxx>
> Signed-off-by: Xi Wang <xi.wang@xxxxxxxxx>
> Signed-off-by: Luke Nelson <luke.r.nels@xxxxxxxxx>

Same here:

Acked-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>

Thanks!